This project involves the molecular genetic analysis of the mechanism of action, specificity, and control of bacteriophage P22 antirepressor. This novel regulatory protein represents a higher order of complexity in mechanisms of regulation of gene expression, since it works by interacting with another regulatory protein, phage repressor. Synthesis of antirepressor is in turn under negative control by unknown mechanisms. The mechanism of action of antirepressor will be studied in a defined in vitro biochemical system using purified bacteriophage lambda repressor and purified P22 antirepressor. The kinetics and stoichiometry of the binding reaction between repressor and antirepressor will be determined. A genetic approach has been used to show that antirepressor synthesis is negatively controlled by two regulatory proteins, the products of genes mnt and arc. As shown by Botstein et al. (J.M.B. 91:439, 1975) and Levine et al. (J.M.B. 91:421 1975), the mnt function represses antirepressor (ant) gene expression in the lysogenic state. I have shown that the arc function negatively regulates antirepressor during infection. The mechanisms by which mnt and arc regulate antirepressor synthesis will be investigated.